How about buying some cheap plastic alternatives first? PartsExpress (Dayton) has 8" waveguide for just a few dollars. Then you might keep your baffle holes more or less the same.
And maybe you'll find the cheap plastic stuff isn't bad at all😀 ( Oh, you might want to smoothen its throat, but nothing major )
And maybe you'll find the cheap plastic stuff isn't bad at all😀 ( Oh, you might want to smoothen its throat, but nothing major )
Minimum order, shipping from the USA, me being extremely poor, the cut-outs are likely to be different. That is why I won't do that, as much as it does appeal. I'm sure those plastic ones are ideal, it's just I'd prefer to see wood there if possible. Should be there soon.
At least you are WAYYYY!! ahead of me Simon; I haven't picked up a router or soldering iron since we started packing and moved house.
At least anothe 3 months until we get established here.
By then I will probably have changed my mind? Again!
At least anothe 3 months until we get established here.
By then I will probably have changed my mind? Again!
Time for an update: I've had a call from my friend who says his Dad's finished making my waveguides!!!! He was busy decorating the house so they were well and truly on the back-burner. I can't wait to see them and check out if they're suitable.
In other news I used two of my Skytronic woofers to get some bass in my car. I put them on a false WBP 18mm plywood parcel shelf... they work quite well!
So I've had to replace them, which I've just done. The brand has changed names so if anyone wants anything like this it's now QTX (still model 902.222 for now). Only real difference is the price has crept up a few £.
Hoping to have more to report soon, this project has been on hold for far too long!
Simon
In other news I used two of my Skytronic woofers to get some bass in my car. I put them on a false WBP 18mm plywood parcel shelf... they work quite well!
So I've had to replace them, which I've just done. The brand has changed names so if anyone wants anything like this it's now QTX (still model 902.222 for now). Only real difference is the price has crept up a few £.
Hoping to have more to report soon, this project has been on hold for far too long!
Simon
Well it's possible I won't even like waveguide or compression tweeter treble... we will see! I can't wait to get cracking on with more work on these now.
If I didn't like the drivers I could always put soft dome tweeters in the 'guides I suppose.
I now need to work out where the acoustic centre is in relation to the midrange driver below so can route out the baffle accordingly.
Where is the acoustic centre on a compression tweeter anyway?
I think for the mid it's where the voicecoil ends behind the dustcap.
I now need to work out where the acoustic centre is in relation to the midrange driver below so can route out the baffle accordingly.
Where is the acoustic centre on a compression tweeter anyway?
I think for the mid it's where the voicecoil ends behind the dustcap.
Ok, I will try to work out where that is in my driver. I will then do some tests with a microphone and 1khz sine wave and try to find the optimum position of the waveguide relative to the mid. I'll connect the drivers out of phase to each other and find the biggest null...
Time alignment
To help me visualise how much of an issue (or not) with time-alignment this design might have I took a bit of my picture (it's to scale where 1 pixel = 2mm) and put some extra details on it.
Ok, this includes some guesswork, but it looks like the difference is just about 1cm or less. The midrange driver is closer to the ear. I don't think I'm going to spend too long worrying about such a small distance. I will concentrate on making the waveguide nicely flush with the baffle to avoid excessive diffraction problems.
Simon
To help me visualise how much of an issue (or not) with time-alignment this design might have I took a bit of my picture (it's to scale where 1 pixel = 2mm) and put some extra details on it.
Ok, this includes some guesswork, but it looks like the difference is just about 1cm or less. The midrange driver is closer to the ear. I don't think I'm going to spend too long worrying about such a small distance. I will concentrate on making the waveguide nicely flush with the baffle to avoid excessive diffraction problems.
Simon
Attachments
I've just been thinking about the taper at the top of my baffles and how to make it look and perform its best. I might use the router on a circle jig to carve the corners off around the wave-guide, leaving maybe 1cm or so around the wave-guide. I might even bevel the edge a little.
Hi Simon, Had not seen this thread b4 and since you are intending to use EnABL on the Beta 8 and woofers, I thought to throw my weight around a bit.
With cone drivers, the addition and control of the cone breakup modes actually occurs out beyond the first mid cone pattern ring, the first big resonance node. As you add more pattern rings out in this area, to control subsidiary resonances, you will begin to bring the high frequencies forward in phase , with reference to the signals at the first mid cone ring set. They will not actually change their FR as the phase is lifted. The Beta 8 has a pretty bad Raleigh wave arising out in the last 1/4 of the cone and damping this is likely to upset the normal phase / time alignment solutions used to match tweeters with mids. I would not make your tweeter placement a fixed item until you have everything else tied down. I may be greatly mistaken, but I think you will find a match in acoustic source depth between the two, to be further forward than you might otherwise find.
Are you going to EnABL the tweeter also? Doing so will make the match somewhat easier as the match point will be very audible in the perception of the imaginary spatial activities, of the music being played. Doing this matching is actually much easier in stereo than in mono and the perfect match will have the "wall" of the window you are listening through go from bent forward or backward to exactly vertical. This is actually using the wide band low amplitude ques for reproduced space, rather than the music itself, as the location finder for the tweeter.
Bud
With cone drivers, the addition and control of the cone breakup modes actually occurs out beyond the first mid cone pattern ring, the first big resonance node. As you add more pattern rings out in this area, to control subsidiary resonances, you will begin to bring the high frequencies forward in phase , with reference to the signals at the first mid cone ring set. They will not actually change their FR as the phase is lifted. The Beta 8 has a pretty bad Raleigh wave arising out in the last 1/4 of the cone and damping this is likely to upset the normal phase / time alignment solutions used to match tweeters with mids. I would not make your tweeter placement a fixed item until you have everything else tied down. I may be greatly mistaken, but I think you will find a match in acoustic source depth between the two, to be further forward than you might otherwise find.
Are you going to EnABL the tweeter also? Doing so will make the match somewhat easier as the match point will be very audible in the perception of the imaginary spatial activities, of the music being played. Doing this matching is actually much easier in stereo than in mono and the perfect match will have the "wall" of the window you are listening through go from bent forward or backward to exactly vertical. This is actually using the wide band low amplitude ques for reproduced space, rather than the music itself, as the location finder for the tweeter.
Bud
Hi Bud,
Thanks for posting your thoughts here, I find the information very interesting.
With regards to time alignment, I am not so sure I have too much choice on adjusting the relationship between treble and mid drivers. The waveguide and Beta 8 are quite neatly flush-mounted to the baffle now. There is perhaps a little room for manoeuvre with the Beta 8 but, to avoid diffraction problems, the waveguide is going to stay put.
I haven't decided what EnABL process, if any, can be applied to the Eminence APT tweeter and/or waveguide. Cosmetics will be a factor with this speaker as the baltic birch plywood is beautiful to behold and I want to keep it beautiful. That would not stop me from sourcing a more subtle shade of brown paint to more closely resemble the original wood (but still be visible to be practical to apply) if EnABL is warrented on the WG exit or throat.
I would value your opinion on my decision to cut or not cut the sides of my baffle to a taper or round top to more closely trace the waveguide shape. I know it could be better sonically but I'm afraid if I mess it up it could be very costly and I have cut the waveguide holes already - meaning there's nowhere to anchor the circle jig on the baffle 🙁
Any thoughts would be appreciated as this is troubling me. With this bridge crossed I can get on with assembling the panels.
Thanks,
Simon
Thanks for posting your thoughts here, I find the information very interesting.
With regards to time alignment, I am not so sure I have too much choice on adjusting the relationship between treble and mid drivers. The waveguide and Beta 8 are quite neatly flush-mounted to the baffle now. There is perhaps a little room for manoeuvre with the Beta 8 but, to avoid diffraction problems, the waveguide is going to stay put.
I haven't decided what EnABL process, if any, can be applied to the Eminence APT tweeter and/or waveguide. Cosmetics will be a factor with this speaker as the baltic birch plywood is beautiful to behold and I want to keep it beautiful. That would not stop me from sourcing a more subtle shade of brown paint to more closely resemble the original wood (but still be visible to be practical to apply) if EnABL is warrented on the WG exit or throat.
I would value your opinion on my decision to cut or not cut the sides of my baffle to a taper or round top to more closely trace the waveguide shape. I know it could be better sonically but I'm afraid if I mess it up it could be very costly and I have cut the waveguide holes already - meaning there's nowhere to anchor the circle jig on the baffle 🙁
Any thoughts would be appreciated as this is troubling me. With this bridge crossed I can get on with assembling the panels.
Thanks,
Simon
One more question if I may - how best might I proceed with applying micro-gloss or diluted PVA glue to the plastic woofers? They are cheap, flimsy and of low-medium Q. I wonder how the application of gloss/PVA might affect their efficiency, stiffness, Q and subjective qualities.
Simon
Simon
First of all you need to consider if the coating will really stick ( in the long term) to the cone. In any case the mass will go up and Fs will go down. That might take the Q down but spread it over a much wider range. That shouldn't be good either ?
Efficiency will certainly go down. HF performance will also go down but you may have to try it to see if this happens in an acceptable way or not. The cone break up modes should shift and trying it out practically is the best way to find out quickly. Wonder if it could make the break up more severe ?
If weighing down the cone is the target , one could just use lead or copper rings near the base of the cone.
Efficiency will certainly go down. HF performance will also go down but you may have to try it to see if this happens in an acceptable way or not. The cone break up modes should shift and trying it out practically is the best way to find out quickly. Wonder if it could make the break up more severe ?
If weighing down the cone is the target , one could just use lead or copper rings near the base of the cone.
Hi,
Thanks for the ideas. I'm not sure what the target is to be honest, I was just thinking aloud there. If applying gloss/glue to the woofers will make them more rigid (and a bit less efficient) then it could be a good thing to do. I'm not going to worry about efficiency too much as already I feel I need to actively biamp these speakers to get the best results. Passive here can work (as indicated by a quick and dirty test with simple x-o) but it will be very inefficient.
Simon
Thanks for the ideas. I'm not sure what the target is to be honest, I was just thinking aloud there. If applying gloss/glue to the woofers will make them more rigid (and a bit less efficient) then it could be a good thing to do. I'm not going to worry about efficiency too much as already I feel I need to actively biamp these speakers to get the best results. Passive here can work (as indicated by a quick and dirty test with simple x-o) but it will be very inefficient.
Simon
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